Guy,s I have a brand new TCI trans. On the left side/rear, there is a large blue plug. My 72 350 trans has a cap on that spot, about the size of a orange with a wire snap ring, pulled it of,and found buckle/with some gears. Do I just remove my 350 cap/ring and place it on my 400? The inside wall is solid, the tci 400 has a hole inside.

The cup/large cap is to big for my 400 tci, and there is no screw on for my mph cabe, is there some other part I haft to buy?

Post a pic.
Sounds like it may be the speedometer hole but can't see it from here.

It,s the hole for the speedo cable, I check another 400, so I will get a used one, or get a gear set up for my 3:55 gear ratio.